What is SIS?  

It’s natural to want to get off the groomed trails when heavy snow starts falling. After all, that’s where the best powder is.

However, if you ski or snowboard off piste during or after heavy snow then you need to be aware of SIS. If you just asked yourself, “What is SIS?” then you need to keep reading our guide here to stay safe while at Mammoth Mountain or any mountain. Check out our short guide below, then visit ASO Mammoth for the best ski and snowboard rentals in Mammoth Lakes!

SIS Defined

SIS stands for snow immersion suffocation. As the name implies, it happens when a skier or snowboarder is trapped under heavy snow and suffocates.

Fortunately, SIS won’t happen on a groomed run since the trails are cleared of powder snow to make a solid surface. However, SIS is a serious danger once you leave the groomed trails where deep powder is left ungroomed and there are trees it can consolidate around.

Where SIS Happens

One of the most common forms of SIS is falling into a tree well.

Tree wells form when heavy snow falls around a tree with large, low branches that prevent the snow from consolidating around the trunk of the tree. Over the course of a season or a heavy storm, tree wells can deepen by several feet and be deep enough to completely cover adults.

If you fall into a tree well while skiing or snowboarding, especially if you go headfirst, then you’ll be at serious risk of suffocating since the loose snow will prevent you from digging yourself out as well as collapse around your airways.

SIS can also happen away from trees if the snow is deep enough, but the main place it happens is around evergreen trees.

How to Avoid SIS 

The best way to avoid SIS is by skiing with a partner if you go off-piste. Even experienced skiers who are in control can still fall into tree wells, and if you do then your best chance of getting out is for your partner to help you.

Always ride with a friend when riding through deep snow!

What To Do if You Fall in a Tree Well

If you fall into a tree well, then you need to get someone’s attention so they can help you get out. That could mean yelling or blowing on a whistle if you have one.

To do either of those things, you need to protect your airway, so do whatever you can to keep your head above the snow. That can mean grabbing branches or the trunk of the tree, but you need to get your head above the snow.

If your head is beneath the snow, then protect your airways by making space around your face with your arms.

If no one has come to help you and you can access your phone, try calling the ski patrol or an emergency number to let someone know where you are and that you need emergency help.